Thermal protection, what are your choices and how do they work?

Wet Suits

A properly fitting wet suit will allow a thin film of water to seep between the suit and your skin. Your body heats this layer of water, and the neoprene foam rubber prevents the surrounding water from cooling that layer. Many people mistakenly believe that the water, once trapped between skin and suit, does not experience any exchange. In other words once the water has got in it stays there and is never replaced with more water from the ocean/river whatever. Not so, a wet suit will have an element of water exchange to it, and the better the wet suit fits, the less this will occur. A shorty version of a wet suit means that the sleeves will stop immediately above the elbow, and the legs immediately above the knee joint.

Semi-dry suits

A slightly different version of a wet suit is commonly called a ’semi-dry’ suit. the key differences here are the level of engineering which has gone into the ankle, wrist and neck seals to eliminate water exchange. Semidry suits are more commonly used in temperate climates where the improved thermal qualities are required for extended submersion, and the user is not electing to wear a dry suit. Some new higher end regular wet suits are more like a semi-dry, featuring a shiny neoprene surface to seal better against the skin. The big difference really being the thickness of the neoprene. A semi-dry suit is generally at least 5mm thick, and maybe even 7mm thick and may even have an attached hood.

Dry Suits

Dry suits, as their name suggests keep the occupant dry. It should be stressed here that ‘dry’ is a relative term and is intended to mean that the wearer does not come into direct contact with the medium in which he or she is immersed. (An example of that may be a police diver who is tasked with searching a large sewer pipe.) Most sport divers interested in the purchase of a dry suit are faced with the choice between compressed neoprene rubber, or a multi-laminate membrane material. My personal favorite is laminate, but I know many divers who prefer neoprene due to it’s increased abrasion resistance. (I am of the school of "take only photos and leave only bubbles" and believe that no diver should touch anything and if they cannot avoid crashing into things, then take a buoyancy control course!) A dry suit operates in conjunction with an undergarment of very high thermal qualities, sometimes referred to as a ‘wooly bear’ due to the appearance of the early versions. My last one was a 1 piece jump suit with a tough nylon outer layer with pockets etc. and a thick thermal pile inner surface. It was worn all day if I was diving or teaching. The dry suit will most likely have a boot attached to the bottom of the leg, meaning that with water tight seals at wrist, and neck the wearer stays dry. Now, it is very common to exit from a dive and be aware of being slightly damp. That is unlikely to be a suit malfunction, it is simply condensed perspiration.

So these are your choices, by all means be guided by other divers, but stick to what feels right. If you dive a lot, then buy the best you can possibly afford I know it pays off. Remember that you should be comfortable, and just because everyone else on the boat is wearing a 3 mm shorty and you have a 5mm full length semi-dry on, so what? Do not allow peer pressure to turn you into a hypothermia case!